Embodiments of the subject matter disclosed herein generally relate to rotary or turbo machines and more particularly to heat management in compressors provided with a dry gas seal.
During the past years, with the increase in price of fossil fuels, the interest in many aspects related to the processing of fossil fuels has increased. During processing of fossil fuels, fluids are transported from on-shore or offshore locations to processing plants for subsequent use. In other applications, fluids may be transported more locally, for example, between sub-systems of a hydrocarbon processing plant to facilitate distribution to end-users.
At least some fluid transport stations use rotary machines, such as compressors, fans and/or pumps that are driven by gas turbines. Some of these turbines drive the associated fluid transport apparatus via a gearbox that either increases or decreases a gas turbine output drive shaft speed to a predetermined apparatus drive shaft speed. In other rotary machines, electrically-powered drive motors, or electric drives are used in place of (or in conjunction with) mechanical drives (i.e., gas turbines) to operate the rotary machine. Regardless of the particular setting, i.e. on-shore, off-shore, etc. and regardless of whether the rotary machine is turbine or motor driven, there is an ever present need to increase the efficiency, decrease the costs, and reduce the environmental impact of fossil fuel processing, and in particular, of rotary machines involved in such processing.
One particular area of concern is heat management. Rotary or turbo machines and compressors in particular, oftentimes require supplemental systems to facilitate heat management, i.e. the removal or addition of heat. Proper heat management has grown even more important with the now prevalent use of high performance components which oftentimes are more sensitive to heat related problems.
For example, many rotary machines now incorporate the use of one or more dry gas seals to improve machine performance and reduce process fluid leakage. Dry gas seals typically include a dry gas seal stator (a non-rotating ring) and a dry gas seal rotor (a rotatable ring). During operation of a rotary machine including a dry gas seal, grooves in the dry gas seal stator and rotor generate a fluid dynamic force causing the dry gas seal stator to separate from the dry gas seal rotor to create a “running gap” between the dry gas seal stator and rotor. The typical “running gap” is quite small, on the order of microns. With such tight tolerances, dry gas seals are particularly vulnerable to damage, particularly when subjected to operating conditions exceeding those for which the dry gas seal was designed.
For example, pressurized process fluids may reach temperatures greater than the temperature range for which the dry gas seal was designed. If the process fluid is particularly hot, even temporary exposure of such pressurized fluids to the dry gas seal may heat the dry gas seal outside the temperature range for which the dry gas seal was designed. It is therefore desirable in certain circumstances to cool the process fluid before the process fluid bears against the dry gas seal.
Low process fluid temperatures also threaten the proper operation of dry gas seals. For example, during episodes of temporary machine shut down, a portion of the process fluid in the proximity of a dry gas seal may undergo an endothermic process, e.g. depressurization, during which the temperature of the process fluid may drop significantly. A precipitant or other non-gaseous matter may thereby be produced in the process fluid. Such precipitants or other non-gaseous matter may have significant hardness and take on the form of a particulate. If such particulates make their way to the dry gas seal at startup, the particulates may, for example, abrade the surfaces of the dry gas seal rotor and/or stator which define the “running gap”. Such damage may necessitate costly machine shut down and repairs. It is therefore also desirable in certain circumstances to heat the process fluid before the process fluid bears against the dry gas seal.
It is also important to note that even if one is able to heat or cool the process fluid, such heating and cooling will oftentimes be ineffective to prevent temperature related damage to the rotary machine, and specifically, the dry gas seal, if the temperature of the process fluid changes faster than one is able to heat or cool the gas. In other words, if the temperature of the process gas changes abruptly, for example, during a pressure surge, and the solution, means, or structure for cooling the process gas is implemented in such a way that the lag time in process fluid temperature response is too great, then, regardless of the attempt to heat or cool the process fluid, the dry gas seal may still be damaged.
Therefore, it is also desirable in certain circumstances to have the option of changing the temperature of the process fluid quickly, particularly, process fluid which may bear against the dry gas seal.